The purpose of the proposed research is to elucidate the functional architecture of the small intestinal microcirculation. The emphasis will be on villus-to-villus heterogeneity of flow, its control, and its relation to absorption, secretion and epithelial nutrition. The required fine spatial resolution will be obtained by the chief method to be employed: direct microscopic localization, counting, and accurate sizing of microspheres, together with visualization of the blood vessels by injection techniques. Data from this approach will be supplemented by observations from other procedures.